Selective relay system



Feb. 14, 1950 v. J. CLARKE SELECTIVE RELAY SYSTEM Filed June 11, 1946 STAGES STAGE 2 STAGE/ Inventor": Varro 1C1 arke,

His Attorney Patented Feb. 14, 1950 SELECTIVE RELAY SYSTEM Varro J. Clarke, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application June 11, 1946, Serial No. 675,874

7 Claims. (Cl. 177353) This invention relates to systems for providing an automatic indication or alarm when a predetermined sequence of signals takes place.

In automatic signal systems, as for example devices to produce an audible alarmv when an SOS signal appears at a radio receiver, it is necessary to provide a highly reliable system capable of producing the desired alarm after a predetermined sequence of signals while at the same time being immune to interfering signals. It is particularly difllcult to achieve this performance in systems intended to operate from a radio receiver inasmuch as the normally high noise level due to atmospheric disturbances and interfering signals tends to cause false operation of the alarm.

It is an object of this invention to provide improved means to produce an automatic alarm after a predetermined sequence of signals.

It is a further object of this invention to provide an automatic alarm having a high degree of freedom from false operation due to undesired signals or noise.

An additional object of this invention is to provide an automatic alarm system that may readily be arranged to operate with any desired degree of freedom from undesired signals, thereby to permit simplification of the system in accordance with the actual conditions encountered in each application.

Yet another object of this invention is to provide an automatic alarm system utilizing standard, low cost, electrical components and which is simple in construction and reliable in operation.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, both as to its organization and method of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which the single figure shows the circuit diagram of an automatic'alarm system incorporating the features thereof.

Referring now to the figure, i represents a source of control signals which may, for example, be a radio receiver tuned to receive signals of predetermined frequency, say 500 kilocycles. The actual voltage appearing across source I consists of various signals including, at the instant the alarm is desired to operate, the sequence of signals representin the combination desired to operate the alarm. Signals from source I are applied to a frequency sensitive relay, shown generally at 2, through the normally closed contacts 5 of a hold-in relay, shown generally at 3. For purposes of explanation, these relays, together with other relays of the circuit, are shown in the unenergized or open position. In the particular embodiment of this invention shown in the figure, relays 2, l0, and I6 assume this position because of gravitational forces and relays 3, Ii, and I! are biased to the positions shown by springs. Frequency sensitive relay 2 is constructed in a manner to be described hereafter to operate only when voltage of predetermined frequency and sufiicient magnitude and duration is applied. When signals appear at source i of frequency and magnitude sufficient to cause operation of relay 2, contacts 9 are closed, thereby connecting the operating coil of relay 3 to source of operating voltage 8. The resulting current flow causes force that overcomes the force of the restraining spring of relay 3, thus closing contacts 4, 6. and I and opening contacts 5.

Of course, the relay makes no connections be-- tween different pairs of contacts but merely connects or disconnects contacts of the same pair. Contacts 4 cause relay 3 to lock in and remain in the closed position independent of operation of relay 2 whereas contacts 5 disconnect relay 2 from source I, thereby opening contacts 9.

The second relay stage includes frequency sensitive relay l0, and hold-in relay ll. Relay I 0 is constructed to operate when the applied voltage has a predetermined frequency value, this value being different from that required to operate relay 2. Relay ID is connected to source i through the normally closed contacts ll of relay II and the normally open contacts 6 of relay 3. When relay 3 is closed, relay I0 is thereby connected to source I and will itself close if signals at source i are of predetermined frequency and sufllcient magnitude and duration. When relay in closet, contacts I! are closed, thus connecting relay H to source of operating voltage 8 and actuating that relay. This closes contacts i3 and I5 and opens contacts I. Contacts i3 thereby cause relay Ii to remain in the closed position independent of the position of relay in and contacts it open the circuit to relay ill thereby causing it to drop out and open contacts II.

The third relay stage consists of frequency sensitive relay l6 and hold-in relay I 1. Relay I6 is constructed to operate on voltage of predetermined frequency, the value of this frequency being different than the frequencies required to operate relays 2 and H). The former relay is connected to source I through the normally closed contacts 20 of relay l1 and the normally open contacts iii of relay ll. When relay H is closed, and signals appear at source I having the correct frequency and suilicient magnitude and duration, relay l6 closes, thereby closing contacts is and connecting relay H to source of operating potential 8. This causes relay I! to close, thereby opening contacts 20 and-2| and closing contacts l9 and 22. Contacts l9, when closed, hold relay I I in the closed position regardless of the position of relay l6 whereas contacts 20 disconnect relay 16 from source I and cause it to drop out, thereby opening contacts 18. Contacts 22, when closed, actuate an alarm device, shown generally at 23.

It is the function of the circuit including relay 24, to prevent operation of alarm 23 unless the signals required to operate relays 2, Hi, and I6 appear within a predetermined time interval. Relay 24 is constructed to open contacts 26 at a predetermined time after energy is initially applied from source 21, this relay being biased to a closed position by gravity. Hence, when contacts I of relay 3 are closed as a result of operation of relay 2, relay 24 is connected to source 21 and this time period commences. If, before this time period elapses, relay I1 is actuated by the desired signals applied to relays i6 and [6, contacts 2| of relay I! are opened and relay 24 never operates. On the other hand if the time period does elapse before operation of relay i1, relay 24 operates and opens contacts 26, thereby disconnecting source 8 from relays 3, ii, and II. This deenergizes these relays and causes them to assume the open position indicated in the figure, thus preparing the system for a normal operating sequence.

The operation of the relays in the various stages of the system may be summarized as follows:

Stage 1.When signals of the frequency of operation and sufflcient magnitude and duration of relay 2 appeara. Relay 3 is closed and stays closed so long as contacts 26 of relay 24 do not open. b. Relay I is connected to source i.

0. Relay 24 is connected to source 21, thereby starting the time period of that relay. Stage 2.When relay 3 is closed and signals of sufllcient magnitude and duration at the frequency for which relay I0 is set appear a. Relay II is closed and remains closed as longas contacts 26 of relay 24 are closed. b. Relay i6 is connected to source I. Stage 3.-When relay H is closed and signals of sufflcient magnitude and duration at the frequency to operate relay l6 appeara. Relay I7 is closed and remains closed as long as contacts 26 of relay 24 do not open.

b. Relay 24 is disconnected from source 21, thereby preventing opening of contacts 26.

0. Alarm 23 is actuated.

In order to restore the system to an operating condition after alarm 23 has been energized;

4 relays and provide a band pass filter passing only the desired frequencies to each one. Alternatively, a simple resonant circuit such as is shown in the drawing may be provided, the resonant circuit utilizing the inherent inductance of the relay coil and a parallel capacitor. When voltage applied to this combination is equal to or very near the resonant frequency, current flow through the relay will build up and reach the value required to close the relay after a time interval determined by the voltage value. When the voltage is of some other frequency, current flow will not build up and the relay will not operate. A further method of providing frequency selective relay action is to use a mechanical system, such as torsional pendulum or a vibrating reed, having a natural frequency equal to that desired to operate the relay and causing the relay current to move the mechanical system. In this case signals of the desired frequency will cause cumulative movement of the pendulum or reed while signals of other frequencies will not have this effect. Any one of these procedures will provide the desired frequency selective action. In general, however, if the frequency desired to operate the relay is relatively high, the resonant circuit will be most satisfactory whereas if the frequency is relatively low, the mechanical system is most effective.

Time delay relay 24 may be any one of the various relays adapted to close contacts at a predetermined time after application of voltage. It may, for example, include a mechanical system such as a dashpot or escapement to prevent closing of contacts 26 until a predetermined time has elapsed after energizing the relay coil. Alternatively, an electrical system, such as that shown in the figure may be used. Inthis case condenser 29 is charged through resistance -28 when relay contacts 1 and 2| are closed, thus causing voltage to build up across this condenser at a rate determined by the R. C. time constant of the system. After a predetermined time, the voltage across condenser 29 will reach the value necessary to operate relay 24 and thus open contacts 26 by overcoming the gravitational forces thereon.

A further degree of freedom from false operation is provided in the above-described embodiment of this invention because relays 2, l0, and I6 have, in addition to their frequency selective action, a time selective action, thereby requiring that each individual operating signal not only be of the correct frequency but of sumcient length and magnitude. The resonant circuit system or pendulum system described above inherently has this characteristic for a period of time is required in each case for the cumulative action of applied voltage to cause operation of the relay. Dashpots, escapements, or similar devices can be used to increase this time delay.

The alarm system of this invention requires a group of signals of predetermined frequencies to cause its operation. In addition, the signals mustpeach be of suflicient duration to actuate relays 2, l0, and I6 and the complete group must take place within a limited period of time. These requirements render the system substantially immune to interfering signals as such signals rarely have the peculiar combination of frequencies and duration required. It is therefore particularly suitable for use in applications such as automatic radio distress systems where interference is severe and reliable operation is essential.

While this invention has been described with reference to the particular embodiment shown in the figure, it will be evident to those skilled in the art that various modifications may be made in accordance with the particular conditions encountered in each application. If for example, the possibility of interference is remote, only two stages in the system may be necessary, one stage responding to one frequency and the second stage responding to another frequency. In this case, decreased complexity and a corresponding reduction in cost is achieved without impairing the performance of the system for the intended purpose. On the other hand, if the system is to be applied where interference is particularly bad, additional stages may be necessary to avoid the possibility of false operation, thereby providing an even greater degree of freedom from interference than that associated with the three stages shown.

While this invention has been shown and described as applied to a particular system of connections and embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing therefrom. In particular it may be applied for purposes other than the radio alarm described and means other than an audible or visual alarm may be operated by the system. I therefore aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an input circuit, a first relay, means to actuate said relay when voltage of predetermined frequency appears at said input circuit, a second relay, means to actuate said second relay when said first relay is actuated, locking means to cause said second relay to remain in the operated condition when once operated, a third relay, means to actuate said third relay when said second relay is actuated and voltage of a second predetermined frequency appears at said input circuit, a utilization device, means to energize said device when said third relay is actuated, and means to restore both said first and second relays to the deenergized condition if a predetermined time interval elapses after operation of said first relay and said third relay has not operated within that interval.

2. In combination, an input circuit, a first relay, means to actuate said relay when voltage of predetermined frequency and at least a predetermined magnitude and duration appears at said input circuit, a second relay, means to actuate said second relay when said first relay is actuated locking means to cause said second relay to remain in the operated condition when once operated, a third relay, means to actuate said third relay when said second relay is actuated and voltage of a second predetermined frequency and at least a predetermined duration and magnitude appears at said input circuit, a utilization device, means to energize said device when said third relay is actuated, a fourth relay constructed to operate after a predetermined time interval following energization. said time interval exceeding the sum of said predetermined durations, means for energizing said time delay relay when said first relay is actuated and for deenergizing it when said third relay is actuated. and means responsive to operation of said time delay relay to restore both said first and second relays to the deenergized condition if said predeterminedtime interval elapses after operation of said first relay and said third relay has not operated within that interval.

3. In combination, a source of wave energy, a plurality of relay stages, means to connect the first of said stages to said source, means to connect each of the remaining of said stages to said source when all of the preceding stages are actuated, locking means to cause said second means to remain in the operating condition when the first of said preceding stages is actuated, means to actuate each of said stages when energy applied from said source thereto is of predetermined frequency, the value of said frequency being different for each stage, a utilization device, means to energize said utilization device when the last of said stages is actuated, and means to deenergize all of said stages if said last stage is not actuated within a predetermined time after actuation of said first stage.

4. In comlination, a source of wave energy having a plurality of selectively different frequencies, a corresponding plurality of frequencyselective relay stages, means to connect the first of said stages to said source, means to connect each of the remaining of said stages to said source when all of the preceding stages are actuated, locking means to cause said second means to remain in the operating condition when once operated, means to actuate each of said stages when energy applied from said source thereto is of predetermined frequency and has at least a predetermined duration and magnitude, the value of said frequency being different for each stage, a utilization device, means to energize said utilization device when the last of said stages is actuated, a time delay relay constructed to operate after a predetermined time interval following energization, said time interval exceeding the sum of said predetermined durations, means for energizing said time delay relay when the first of said stages is actuated and for deenergizing it when the last of said stages is actuated, and

r means responsive to operation of said time delay relay to deenergize all of said stages if said last stage is not actuated within said predetermined time interval after actuation of said first stage.

5. In combination, a source of wave energy, a first relay, means to operate said first relay when the energy of said source is of predetermined frequency, a second relay, means to operate said second relay when said first relay operates, locking means to cause said second relay to remain in the operated condition when once operated, a third relay, means to connect said third relay to said source when said second relay is operated, means to operate said third relay when energy of said source is of a second predetermined frequency, a fourth relay, means to operate said fourth relay when said third relay operates, means to disable said locking means if said fourth relay is not actuated within a predetermined time after said first relay, a utilization device, and means to energize said utilization device when said fourth relay is operated.

6. In combination, a source of wave energy of selectively different frequencies, a first frequencyselective, time-delay relay, means to operate said first relay when the energy of said source is of predetermined frequency and at least a predetermined magnitude and duration, a second relay, means to operate said second relay when said first relay operates, locking means to cause said second relay to remain in the operated condition 7 when once operated, a third, frequency-selective, time-delay relay, means to connect said third relay to said source when said second relay is operated, means to operate said third relay when energy of said source is of a second predetermined frequency and at least a predetermined magnitude and duration, a fourth relay, means to operate said fourth relay when said third relay operates, a fifth time-delay relay constructed to operate, when energized, only after a predetermined time exceeding the sum of said durations, means to energize said fifth relay when said first relay is operated, means controlled by operation of said fifth relay to disable said locking means if said fourth relay is not operated within said predetermined time after said first.

relay, a utilization device, and means to energize said utilization device when said fourth relay is actuated.

7. A selective relay system comprising means for selectively supplying electrical waves having any one of a plurality of different control fre-.

and for time intervals at least equal to the requencies, a plurality of frequency-selective relays each resonant to a different one of said frequencies and constructed to operate after a deflnite time delay following energization at its resonant frequency, means for causing said relays to operate in sequence only when said signals are received in a predetermined frequency sequence constructed to operate, when energized, only after a time period exceeding the sum of said definite time delays, means to energize said longtime-delay relay when the first resonant relay in said sequence is operated and to deenergize it when the last resonant relay in said sequence is operated, means to deenergize all said resonant relays when said long-time-delay relay operates, and a signalling device controlled by operation of said last resonant relay.

VARRO J. CLARKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,943,475 Gurley Jan. 16, 1934 2,008,909 Hershey July 23, 1935 2,255,162 Hart Sept. 9, 1941 2,411,091 Henderson Nov. 12, 1946 FOREIGN PA'IENTS Number Country Date 172,321 Great Britain Nov. 2, 1922 

